Electrical resonators are widely incorporated in modern electronic devices. For example, in wireless communications devices, radio frequency (RF) and microwave frequency resonators are used in filters, such as filters having electrically connected series and shunt resonators forming ladder and lattice structures. The filters may be included in a duplexer (diplexer, triplexer, quadplexer, quintplexer, etc.) for example, connected between an antenna (there could be several antennas like for MIMO) and a transceiver for filtering received and transmitted signals.
Various types of filters use mechanical resonators, such as surface acoustic wave (SAW) resonators. The resonators convert electrical signals to mechanical signals or vibrations, and/or mechanical signals or vibrations to electrical signals.
While certain surface modes are desired, certain standing spurious modes can exists between the opposing faces of the piezoelectric material of the SAW resonator. These spurious modes are parasitic, and can impact the performance of filters comprising SAW resonators.
What is needed, therefore, is a SAW resonator structure that overcomes at least the shortcomings of known SAW resonators described above.